The present invention relates to a vehicular navigation system by which it is possible to search for the optimal route from the present position of the automotive vehicle to a destination and to guide the vehicle along the optimal route to the destination.
The vehicular navigation system searches for a route from the present position or from the starting point to the destination based on input of data such as destination data and suggests a route according to the searched optimal route, thus providing a driver with information on the route to the destination while the driver is driving the vehicle on an unknown or an unfamiliar route. In this route searching, if the driver encounters traffic congestion or traffic restriction on the way, the optimal route can be searched again.
For example, it is proposed in JP-A-7-182596 and JP-A-62-95423 that, in case traffic information such as traffic jam information is received and a congested section point is detected ahead on the optimal route already set, an attempt is made to avoid passing through the congested section or to make it difficult to pass through the congested section by increasing cost (e.g. length) of road data of that section and to search again for another route to avoid the congested section. In JP-A-6-186049, it is disclosed that a route from the present position to the destination is searched again with respect to the route already suggested by adding VICS (Vehicle Information & Communication System) information.
In the system as disclosed by the above JP-A-7-182596 and JP-A-62-95423, only where there is traffic jam information for the already suggested route, is the road data of the route updated and the route searched again. In case traffic jam information is detected on a route ahead in the advancing direction during route guidance and the destination can be reached earlier if the vehicle runs along a byroad or makes a detour, the system is effective to find such a byroad or a detour. However, when the presently suggested route has been searched by adding traffic jam information and the search results suggest need to make a detour of a main road because the main road, usually not jammed, is currently jammed because of construction work or traffic accident as shown in FIG. 15(A), and in case the traffic jam has been already dissolved while the vehicle was running along the already suggested route, such information is not given even though the vehicle can reach the destination earlier by running along the main road.
Also, the system proposed in JP-A-6-186049 is disadvantageous in that much time is required for searching the route because re-searching must be carried out by adding traffic jam information on a wide area including the present position and the destination, and traffic jam information of zones remote from the present position and unnecessary for the searching is also added.
Incidentally, VICS is now in the stage of practical application and its service area is gradually expanding. Thus, it is an important problem how efficiently real-time road traffic information can be utilized for searching for an optimal navigation route within a short time.